Nowadays, applications of navigating technologies have gradually extended from purely the professional military aviation and voyage applications to commercialized applications. This is primarily attributed to rapid development of the Global Positioning System (GPS). In recent years, GPS has been widely applied in vehicles and personal navigation systems; and especially, among various consumer electronic products, personal navigation devices (PNDs) have become daily necessities in general people's life. In other words, commercialized satellite positioning applications have been now widely accepted by the general people.
Generally speaking, the positioning deviation of current GPS devices is within about 10 meters. Because such a positioning deviation is inadequate in urban areas with dense road networks, most PNDs are equipped with an electronic map so that, in conjunction with an appropriate algorithm, a road where the user is located can be properly determined. For example, a car driving in an urban area mostly drives along a same road, and it is impossible for the car to instantaneously jump to another road 10 meters apart in reasonable cases.
Therefore, even when a deviation (i.e., an absolute deviation) at the outset of the positioning is as large as 10 meters, the user can still be positioned to be on the same road through use of the electronic map and the appropriate algorithm as long as the deviation (i.e., the relative deviation) is kept at an initial level instead of varying suddenly. However, if the relative deviation varies suddenly, it will be possible that the positioning coordinates obtained at a previous time point and those obtained at a next time point are discontinuous or vary greatly from each other even if the absolute deviation becomes smaller; consequently, this will cause an instantaneous shift in the positioning coordinates. Accordingly, the relative deviation is an important indicator for navigating technologies.
Inevitably, a change in the amount of GPS positioning satellites (or a change in geometry of the GPS positioning satellites) tends to cause an instantaneous positioning coordinate shift. In order to overcome the aforesaid problem, the conventional GPS positioning technology adopts a differential correction algorithm to improve the positioning accuracy of GPS and, together, reduce variations in the accuracy (i.e., reduce the relative deviation in positioning). However, for common commercial GPS devices (e.g., PNDs), they are unable to receive differential correction signals.
Additionally, GPS positioning devices capable of receiving differential correction signals are mostly devices for measurement purpose. These GPS positioning devices not only are relatively expensive, but also typically have to be equipped with other data links in order to receive the differential correction signals; for example, they have to work with the Global System for Mobile Communications (GSM), Wireless Fidelity (Wi-Fi) or the Third Generation Mobile Communications. Further even for a GPS positioning device capable of receiving differential correction signals, the problem of instantaneous positioning coordinate shift may also be caused when a differential correction signal from one of the satellites disappears suddenly. For these reasons, the differential correction algorithm fails to be widely applied in the current GPS positioning devices.
Specifically, to eliminate the instantaneous positioning coordinate shift caused by a change in the satellite amount, the conventional GPS positioning technology has to calculate positioning solutions of satellite configurations before and after a change occurs in the satellite amount; only in this way can the positioning offset caused by the change in the satellite amount be derived so as to eliminate the positioning deviation. Furthermore, for the conventional GPS positioning technology, it takes a long time to calculate necessary positioning coordinates, which indirectly makes it inconvenient for the user to obtain the positioning coordinates.
In view of this, an urgent need exists in the art to reduce the relative deviation by more effectively eliminating instantaneous shift of positioning coordinates received by GPS devices that is caused by an instantaneous change in the satellite amount.